title: A thermogenic secondary sexual character in male sea lamprey.
abstract: Secondary sexual characters in animals are exaggerated ornaments or weapons for intrasexual competition. Unexpectedly, we found that a male secondary sexual character in sea lamprey (Petromyzon marinus) is a thermogenic adipose tissue that instantly increases its heat production during sexual encounters. This secondary sexual character, developed in front of the anterior dorsal fin of mature males, is a swollen dorsal ridge known as the 'rope' tissue. It contains nerve bundles, multivacuolar adipocytes and interstitial cells packed with small lipid droplets and mitochondria with dense and highly organized cristae. The fatty acid composition of the rope tissue is rich in unsaturated fatty acids. The cytochrome c oxidase activity is high but the ATP concentration is very low in the mitochondria of the rope tissue compared with those of the gill and muscle tissues. The rope tissue temperature immediately rose up to 0.3°C when the male encountered a conspecific. Mature males generated more heat in the rope and muscle tissues when presented with a mature female than when presented with a male (paired t-test, P<0.05). On average, the rope generated 0.027±0.013 W cm(-3) more heat than the muscle in 10 min. Transcriptome analyses revealed that genes involved in fat cell differentiation are upregulated whereas those involved in oxidative-phosphorylation-coupled ATP synthesis are downregulated in the rope tissue compared with the gill and muscle tissues. Sexually mature male sea lamprey possess the only known thermogenic secondary sexual character that shows differential heat generation toward individual conspecifics.
authors.affiliation: Department of Fisheries and Wildlife, Michigan State University, East Lansing, MI 48824, USA.
authors.forename: Yu-Wen
authors.initials: YW
authors.lastname: Chung-Davidson
authors.forename: M Cody
authors.initials: MC
authors.lastname: Priess
authors.forename: Chu-Yin
authors.initials: CY
authors.lastname: Yeh
authors.forename: Cory O
authors.initials: CO
authors.lastname: Brant
authors.forename: Nicholas S
authors.initials: NS
authors.lastname: Johnson
authors.forename: Ke
authors.initials: K
authors.lastname: Li
authors.forename: Kaben G
authors.initials: KG
authors.lastname: Nanlohy
authors.forename: Mara B
authors.initials: MB
authors.lastname: Bryan
authors.forename: C Titus
authors.initials: CT
authors.lastname: Brown
authors.forename: Jongeun
authors.initials: J
authors.lastname: Choi
authors.forename: Weiming
authors.initials: W
authors.lastname: Li
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D000273:Adipose Tissue / Q000502:physiology* / Q000648:ultrastructure; D000818:Animals; D003576:Electron Transport Complex IV / Q000378:metabolism; D005227:Fatty Acids / Q000378:metabolism; D008401:Gas Chromatography-Mass Spectrometry; D005786:Gene Expression Regulation / Q000502:physiology*; D007150:Immunohistochemistry; D008297:Male; D046529:Microscopy, Electron, Transmission; D048428:Petromyzon / Q000502:physiology*; D010802:Phylogeny; D060888:Real-Time Polymerase Chain Reaction; D012727:Sex Characteristics; D012726:Sexual Behavior, Animal / Q000502:physiology*; D022722:Thermogenesis / Q000502:physiology*; D059467:Transcriptome
chemical_list: D005227:Fatty Acids; D000255:Adenosine Triphosphate; D003576:Electron Transport Complex IV
keywords: Petromyzon marinus; electron transport chain; sea lamprey; sexual character; thermogenic; uncoupling protein